Final answer:
New contract negotiations between local IBEW unions and NECA chapters typically occur every three to five years. The most common negotiation intervals provided in the options are every three years or a combination of every two and every three years. Option c is correct.
Step-by-step explanation:
The frequency of new contract negotiations between local International Brotherhood of Electrical Workers (IBEW) unions and National Electrical Contractors Association (NECA) chapters can vary depending on the specific circumstances of each local union and chapter.
However, typically these contracts, known as Collective Bargaining Agreements (CBAs), are negotiated every three to five years. Since the options provided do not include a five-year duration and negotiation frequency can depend on several factors including industry standards, local preferences, and previous agreements, the closest answer to the general practice would be either every three years (c) or a combination of every two and every three years (d). Despite occasionally occurring every two years, a three-year interval is quite common, making (c) a likely choice.